Triboelectric Nanogenerator for Harvesting Broadband Kinetic Impact Energy

ABSTRACT

A triboelectric generator includes a first triboelectric member, which includes a first conductive layer and an insulating triboelectric material layer disposed on the first conductive layer. The triboelectric material layer includes a first material having a first position on a triboelectric series. An elastic member, disposed against the triboelectric material layer of the triboelectric member and includes a second conductive material, has an elasticity that results in the elastic member being deformed when compressed and returning to an original non-deformed shape after being compressed. The second conductive material has a second position on the triboelectric series. A first load is coupled to the first conductive layer and with the second conductive material so that when a force compresses the elastic member charges will flow between the first conductive layer and the second conductive layer through the load.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/163,692, filed May 19, 2015, the entirety ofwhich is hereby incorporated herein by reference.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under agreement No.DE-FG02-07ER46394, awarded by the Department of Energy. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to generators and, more specifically, to asystem for generating voltage and current using the triboelectriceffect.

2. Description of the Related Art

Energy harvesting by converting ambient energy into electricity mayoffset the reliance of small portable electronics on traditional powersupplies, such as batteries. When long-term operation of a large numberof electronic devices in dispersed locations is required, energyharvesting has the advantages of outstanding longevity, relativelylittle maintenance, minimal disposal and contamination.

When two materials, at least one of which is non-conducting, come intocontact with each other, a chemical bond, known as adhesion, is formedbetween the two materials. Depending on the triboelectric properties ofthe materials, one material may “capture” some of the electrons from theother material. If the two materials are separated from each other, acharge imbalance will occur. The material that captured the electronwill negatively charged and the material that lost an electron will bepositively charged. This charge imbalance gives rise to what issometimes referred to as “static electricity.” The term “static” in thiscase is somewhat deceptive, as it implies a lack of motion when inreality motion is necessary for charge imbalances to flow. The spark onefeels upon touching a door knob is an example of such flow.

The triboelectric effect is a type of contact electrification in whichcertain materials become electrically charged after they come intocontact with another such as through friction. It is the mechanismthough which static electricity is generated. The triboelectric effectsassociated electrostatic phenomena are the most common electricalphenomena in daily life, from walking to driving. However, thetriboelectric effect has been largely ignored as an energy source forelectricity. Some electrostatic micro-generators have been developed andused in research relating to micro-electro-mechanical systems (MEMS),but such designs rely on an extra voltage source to charge electrodeplates instead of harnessing triboelectric effect, leading tocomplicated structures and fabrication processes.

Previously demonstrated triboelectric generators require periodiccontact and vertical separation of two materials that have oppositetriboelectric polarities, making it only applicable to harvest energyfrom intermittent impact or shock. Such systems typically include acavity with a constantly changing volume, which makes packagingdifficult and limits applications in atmospheres with high humidity,corrosive chemicals or gases, and in water or other liquids.

Mechanisms using piezoelectric, electrostatic or electromagneticprinciples to harvest energy from random vibrations, wind flow, airpressure, or human body motions have been developed and applied asgenerators or self-powered sensors. Recently, the development oftriboelectric nanogenerators (triboelectric generators) offers a newparadigm for fabricating high-output and cost effective generators fordriving small electronics. Reciprocating motion is a very commonmechanical motion occurs in natural oscillations, motion of waves, swingof human limbs, and mechanical piston movements, etc. Features of thesemotions that include long reciprocating distance, low frequencies andamplitude or frequency fluctuations pose challenges for previouslydeveloped vibration-harvesters, which were only suited to low-amplitudeand high-frequency excitations induced by inertia forces.

Therefore, there is a need for a reliable, small and easily manufacturedsystem for harvesting triboelectric energy from reciprocating motion.

SUMMARY OF THE INVENTION

The disadvantages of the prior art are overcome by the present inventionwhich, in one aspect, is a triboelectric generator that includes a firsttriboelectric member. The first triboelectric member includes a firstconductive layer and an insulating triboelectric material layer disposedon the first conductive layer. The triboelectric material layer includesa first material that has a first position on a triboelectric series. Anelastic member is disposed against the triboelectric material layer ofthe triboelectric member and includes a second conductive material. Theelastic member has an elasticity that results in the elastic memberbeing deformed when compressed and returning to an original non-deformedshape after being compressed. The second conductive material has asecond position, different from the first position, on the triboelectricseries. A first load is in electrical communication with the firstconductive layer and with the second conductive material so that when aforce drives the first triboelectric member against the elastic member,thereby compressing the elastic member, and after the force is releasedfrom the first triboelectric member, charges will flow between the firstconductive layer and the second conductive layer through the load.

In another aspect, the invention is an electrical generator thatincludes a first triboelectric member, which includes a first conductivelayer and a triboelectric material layer disposed on the firstconductive layer. The triboelectric material layer includes a pluralityof nanoscale protrusions extending outwardly therefrom. Thetriboelectric material layer includes a first material that has a firstposition on a triboelectric series. An elastic member has an undulatedshape and is disposed against the triboelectric material layer of thetriboelectric member. The elastic member includes a dielectric layer anda second conductive layer disposed on the dielectric layer. Thedielectric layer has an elasticity that results in the elastic memberreturning to the undulated shape after being compressed. The secondconductive layer includes a second material that has a second position,different from the first position, on the triboelectric series. A firstload is in electrical communication with the first conductive layer andwith the second conductive layer so that when a force drives the firsttriboelectric member against the elastic member, thereby compressing theelastic member, and after the force is released from the firsttriboelectric member charges will flow between the first conductivelayer and the second conductive layer through the load. A secondtriboelectric member is spaced apart from the first triboelectric memberand includes a fourth conductive layer and a triboelectric materiallayer that is disposed on the third conductive layer. The triboelectricmaterial layer includes a plurality of nanoscale protrusions extendingoutwardly therefrom. The triboelectric material layer includes the firstmaterial. The second triboelectric member is disposed so that theplurality of nanoscale protrusions of the first triboelectric memberface the plurality of nanoscale protrusions of the second triboelectricmember and so that the elastic member is disposed there-between. Afourth conductive layer is disposed on the dielectric layer oppositefrom the second conductive layer. A second load is in electricalcommunication with the third conductive layer and with the fourthconductive layer.

In yet another aspect, the invention is a method of making atriboelectric generator, in which a first conductive layer is applied ona selected surface of a first substrate. A triboelectric material isapplied on the conductive layer. The triboelectric material layerincludes a first material that has a first position on a triboelectricseries. Application of the triboelectric material to the conductivelayer generates a first triboelectric member. An elastic member isgenerated by applying a second conductive layer is applied to adielectric elastic material having a predefined shape. The secondconductive layer includes a second material that has a second position,different from the first position, on the triboelectric series. Thedielectric elastic material has an elasticity that results in theelastic member returning to the predefined shape after being compressed.The second conductive layer of the elastic member is placed against thetriboelectric material of the first triboelectric member. A load iselectrically coupled between the first conductive layer and the secondconductive layer.

These and other aspects of the invention will become apparent from thefollowing description of the preferred embodiments taken in conjunctionwith the following drawings. As would be obvious to one skilled in theart, many variations and modifications of the invention may be effectedwithout departing from the spirit and scope of the novel concepts of thedisclosure.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIGS. 1A-1B are schematic diagrams showing an embodiment of atriboelectric generator with an undulated elastic member.

FIG. 1C is a schematic diagram showing one method of forming anundulated elastic member.

FIGS. 2A-2C is a series of schematic diagrams demonstrating currentgeneration with a device according to the embodiment shown in FIGS.1A-1B.

FIG. 3 is a schematic diagram of a triboelectric generator employing asingle triboelectric member.

FIGS. 4A-4C is a series of schematic diagrams showing an embodimentemploying an elastic member with partial spheres and operation of thisembodiment.

FIG. 4D is a cross-sectional diagram of a partial sphere employed in anelastic member.

FIGS. 5A-5I is a series of schematic diagrams demonstrating one methodof making an elastic member employing partial spheres.

FIG. 6 is a micrograph of a nanoscale protrusions extending outwardlyfrom a triboelectric material.

FIG. 7 is a micrograph of an elastic member employing partial spheres.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the invention is now described in detail.Referring to the drawings, like numbers indicate like parts throughoutthe views. Unless otherwise specifically indicated in the disclosurethat follows, the drawings are not necessarily drawn to scale. As usedin the description herein and throughout the claims, the following termstake the meanings explicitly associated herein, unless the contextclearly dictates otherwise: the meaning of “a,” “an,” and “the” includesplural reference, the meaning of “in” includes “in” and “on.” Also, asused herein, “PTFE” means polytetrafluoroethylene, “PDMS” meanspolydimethylsiloxane, and polyimide is a material commercially known as“Kapton.”

U.S. Pat. No. 9,178,446, filed by Wang et al. on Nov. 3, 2015 disclosesa triboelectric generator and methods of making the same and is herebyincorporated by reference. U.S. Patent Publication Nos.US-2016-0040648-A1 (published on Feb. 11, 2016), US-2015-0070392-A1(published on Mar. 10, 2016) and US-2016-0065091-A1 (published on Mar.3, 2016), all filed by Wang et al., disclose triboelectric generatorsthat employ contact triboelectrification and are hereby incorporated byreference.

As shown in FIGS. 1A-1B, one embodiment of a triboelectric generator 100includes a first triboelectric member 110, a second triboelectric member130 and an elastic member 120 having an undulated shape (such as a wavyshape) disposed there-between. The first triboelectric member 110 andthe second triboelectric member 130 each include a substrate 112 (suchas an acrylic substrate) and a conductive layer 114 (such as a copperlayer) disposed thereon. A triboelectric material layer 116 is disposedon the conductive layer 114. The triboelectric material layer 116 ismade from an insulating material (such as PTFE) that has a firstposition on a triboelectric series. The triboelectric material layer 116has a plurality of nanoscale protrusions 118 extending outwardly from atriboelectric material.

The elastic member 120 includes a dielectric elastic material layer 124(such as a polyimide film, which in one example is Kapton available fromDuPont) that has an elasticity that results in the elastic member 120being deformed when compressed and returning to an original non-deformedshape after being decompressed. Each side of the elastic material layer124 is coated with a second conductive material layer 122 (which caninclude, for example, copper) that includes a material having a secondposition, different from the first position, on the triboelectricseries.

As shown in FIG. 1C, the elastic member 120 can be formed in anundulated wavy shape by weaving the elastic material layer 124 betweenparallel metal rods 140 and heating the elastic material layer 124 tothe glass transition temperature of the elastic material layer 124 andthen cooling the elastic material layer 124 to below the glasstransition temperature. Once cooled, the elastic material layer 124 willmaintain its wavy shape.

One experimental embodiment included a 125 μm thick Kapton film, a 125μm thick PTFE film, a 1/16″ thick acrylic substrate and copper. Firstly,the Kapton film was periodically bent into a wavy shape by using a setof metal rods (with diameter of ¼″). Then the set was sent into a muffleoven and baked at 360° C. for 4 hours. Since Kapton film isthermoplastic, it will remain in the wavy shape stably below its glasstransition temperature. Then a 200 nm copper layer was sputtered on bothsides of the wavy Kapton film as electrodes. Secondly, two slides ofPTFE films were prepared by applying inductively coupled plasma (ICP)etching (specifically 15 sccm Ar, 10 sccm O₂ and 30 sccm CF4 under 400 WRF power and 100 W bias power) on one side of the films andnanostructures were thus obtained, which enhancecontact-electrification. Then, a 200 nm thick layer of copper wassubsequently sputtered on the other side of the film acting aselectrodes. The copper side of the PTFE films was then tightly adheredto two acrylic substrates respectively by using a thin layer of curedPDMS. By sandwiching the Cu-Kapton-Cu wavy core using the two acrylicsubstrates with PTFE films facing inside and bonding the structurestogether with electrical tapes, the final device structure was obtained.

Operation of this embodiment is shown in FIGS. 2A-2C, in which a load210 is electrically coupled between the conductive layers of thetriboelectric members 110 and 130 and the conductive layers of theelastic member 120. Initially, as shown in FIG. 2A, the system is atrest and all of the charges are in balance. As shown in FIG. 2B, when aforce is applied to the system (as represented by the arrow), the systemcompresses the elastic member 120, which causes increased surface areacontact between the elastic member 120 and the triboelectric members 110and 130. This results in triboelectric charge transfer there-between andcurrent flow through the loads 210. When the compressive force isremoved, as shown in FIG. 2C, the elastic member 120 returns to itsat-rest shape, which reduces contact surface area with the triboelectricmembers 110 and 130, and which results in a charge imbalance. Thisresults in reverse current flowing through the loads 210 to return thesystem to electrical equilibrium.

In operation, once the acrylic substrate is under impact, the wavy corewill be compressed in the vertical direction and be extended in thehorizontal direction, converting the vertical compressing force intolateral friction between the core and both PTFE surfaces. Also thecontact area between PTFE and Cu film is increased and the averagedistance between the two is reduced. Once the impact is removed, thewavy core will retract on the horizontal direction and extend on thevertical direction, also leading to lateral friction between the coreand both PTFE surfaces. Also the contact area between PTFE and Cu filmis reduced and the average distance between the two is increased. Theworking process of triboelectric generator includes two parts: thecharge transfer and charge separation. The transfer is accomplished bythe lateral friction between the copper thin films, which loseelectrons, and the PTFE films, which gain electrons. The chargeseparation process is accomplished by the change of capacitance betweenthe copper coated on Kapton film and the copper coated on the back sideof the PTFE films.

As shown in FIG. 3, a triboelectric generator can be made with a singletriboelectric member. In this embodiment, the elastic member 310 isplaced against a second substrate 310.

This embodiment is based on a wavy structured Cu-Kapton-Cu filmsandwiched between two flat nanostructured PTFE films for harvestingenergy due to mechanical vibration, impacting and compressing using thetriboelectrification effect. This structure design allows thetriboelectric generator to be self-restorable after impact without theuse of extra springs and converts direct impact into lateral sliding,which is proved to be a much more efficient friction mode for energyharvesting. In one experimental embodiment, vibrational energy from 5 Hzto 500 Hz was harvested and the generator's resonance frequency wasdetermined at ˜100 Hz at a broad full width at half maximum (FWHM) ofover 100 Hz, producing an open-circuit voltage of up to 72 V, ashort-circuit current of up to 32 μA and a peak power density of 0.4W/m2. The wavy structure of the triboelectric generator can be easilypackaged for harvesting the impact energy from water waves, clearlyestablishing the principle for ocean wave energy harvesting. Consideringthe advantages of triboelectric generator, such as cost-effectiveness,light weight and easy scaling up, this approach might open thepossibility for seeking green and sustainable energy from the oceanusing nanostructured materials.

To study the ability of triboelectric generator to power external loads,one experimental embodiment was tested at 100 Hz under variable loadresistance. An adjustable resistor was used as the load, providingresistance from as low as 1 KΩ to as high as 100 MΩ. The electrometerwas connected in parallel with the resistor to measure the outputvoltage and was connected in series with the resistor to measure theoutput current. It was found that output voltage increases withincreasing load resistance while the output current increases withdecreasing load resistance. Instantaneous peak power density, calculatedby Pd=I2R/S, demonstrated that the highest peak power density of 0.4W/m2 was obtained at the load resistance of 5 MΩ.

As shown in FIGS. 4A-4C, one embodiment of a triboelectric generator 400includes an elastic member that employs an elastic member 424 that has aplurality of three-dimensional shapes extending upwardly from a copperlayer in which each of the three-dimensional shapes having an outersurface that includes copper. In the embodiment shown, thethree-dimensional shapes are partial spheres 426, which are in contactwith the triboelectric material layer 416 (such as PTFE) of thetriboelectric member 410. As shown in FIG. 4D, each partial sphere 426can include a PDMS core 430 with a copper coating layer 432. Returningto FIGS. 4A-4C, the triboelectric member 410 includes a substrate 412, aconductive layer 414 and a triboelectric material layer 416. The elasticmember 424 is mounted on a substrate 420. When a compressive force isapplied, as shown in FIG. 4B, the partial spheres 426 are compressed,thereby increasing their contact surface area with the triboelectricmaterial layer 416, which results in contact electrification and currentflow through the load 210. Eventually, the partial spheres 426 willbecome maximally compressed, as shown in FIG. 4C. Decompression of thesystem will cause the partial spheres 426 to return to their undeformedshape and reverse current to flow through the load 210 during thedecompression process.

As shown in FIGS. 5A-5I, one method for making the partial spheresincludes: treating a silicon or quartz substrate 510 with oxygen plasmato flatten its surface and placing a layer of closely packed polystyrenespheres 512 on the substrate 510. (One method for placing spheres on asubstrate is disclosed in U.S. Pat. No. 7,351,607, issued to Wang et al.on Apr. 1, 2008, which is hereby incorporated by reference.)(Experimentally, polystyrene spheres of the following diameters wereused: 90 μm, 600 μm, and 3 mm.) A PDMS slurry 514 is placed around thespheres 512 and the PDMS slurry 514 is cured. The cured PDMS layer 514is lifted from the spheres 512, thereby leaving a PDMS mold 516 of thespheres. A conductive material layer coating 518 is applied to the mold516 and a second PDMS slurry 520 is applied to the mold 516. The PDMS520 is cured and removed from the mold 514, thereby leaving the elasticpartial spheres 522 employed in the elastic member of the triboelectricgeneration.

In operation, at the initial state, the top area of Cu-depositedhemispheres-array-structured film created a point of contact with PTFEfilm, where there is no charge transfer, which results in no electricpotential. When a compressive force is applied to the device, theCu-deposited hemispheres-array-structured film starts to be deformed anddimensional flat contact area is created with PTFE film accordingly. Thecontact area between the hemispheres-array-structured film and PTFE filmdepends on the applied compressive force. Positive triboelectric chargeson the surface of hemispheres-array-structured film, and negativetriboelectric charges on the PTFE film are created by the triboelectriceffect. At this stage, the device remains in electrostatic equilibriumstate due to negligible dipole moment. As compression on the device isreleased, a strong dipole moment is formed due to the electrostaticeffect, which results in an electrical potential difference between thebottom and top electrodes. Because the Cu-depositedhemispheres-array-structured film has a higher potential than the top Alelectrode, electrons start to flow from the top electrode to the bottomelectrode through the external circuit to neutralize the negativetriboelectric charges in the top electrode, which results in electricsignal observed from the device.

Output performance of the device is determined by two dominant effects.One is the triboelectric effect that is created by periodic contactsbetween two materials that differ in polarity of triboelectricity.Another one is the electrostatic effect that is made by the potentialdifference between two charged materials when those are mechanicallyseparated.

A micrograph of the nanoscale texture applied to the triboelectricmember in the embodiment of FIG. 1A is shown in FIG. 6. A micrograph ofthe partial spheres used in the embodiment of FIG. 4A is shown in FIG.7.

The above described embodiments, while including the preferredembodiment and the best mode of the invention known to the inventor atthe time of filing, are given as illustrative examples only. It will bereadily appreciated that many deviations may be made from the specificembodiments disclosed in this specification without departing from thespirit and scope of the invention. Accordingly, the scope of theinvention is to be determined by the claims below rather than beinglimited to the specifically described embodiments above.

What is claimed is:
 1. A triboelectric generator, comprising (a) a firsttriboelectric member, including a first conductive layer and aninsulating triboelectric material layer disposed on the first conductivelayer, the triboelectric material layer including a first material thathas a first position on a triboelectric series; (b) an elastic memberdisposed against the triboelectric material layer of the triboelectricmember, including a second conductive material, the elastic memberhaving an elasticity that results in the elastic member being deformedwhen compressed and returning to an original non-deformed shape afterbeing compressed, the second conductive material having a secondposition, different from the first position, on the triboelectricseries; and (c) a first load that is in electrical communication withthe first conductive layer and with the second conductive material, sothat when a force drives the first triboelectric member against theelastic member, thereby compressing the elastic member, and after theforce is released from the first triboelectric member charges will flowbetween the first conductive layer and the second conductive layerthrough the load.
 2. The triboelectric generator of claim 1, wherein theelastic member has an undulated shape.
 3. The triboelectric generator ofclaim 1, wherein the elastic member includes a dielectric layer disposedadjacent to the second conductive material.
 4. The triboelectricgenerator of claim 3, wherein the dielectric layer comprises a polyimidefilm.
 5. The triboelectric generator of claim 1, wherein thetriboelectric material comprises PTFE and wherein the second conductivematerial comprises copper.
 6. The triboelectric generator of claim 1,further comprising a plurality of nanoscale protrusions extendingoutwardly from the triboelectric material.
 7. The triboelectricgenerator of claim 1, wherein the first triboelectric member furthercomprises a substrate on which the first conductive layer is disposed.8. The triboelectric generator of claim 1, wherein the first conductivelayer comprises copper and wherein the insulating triboelectric materiallayer comprises PTFE.
 9. The triboelectric generator of claim 1, whereinthe elastic member includes a plurality of three dimensional shapesextending upwardly from a copper layer, each of the three dimensionalshapes having an outer surface that includes copper.
 10. Thetriboelectric generator of claim 9, wherein each of the threedimensional shapes has a PDMS core.
 11. The triboelectric generator ofclaim 9, wherein each of the three dimensional shapes has a partiallyspherical shape.
 12. An electrical generator, comprising: (a) a firsttriboelectric member, including a first conductive layer and atriboelectric material layer disposed on the first conductive layer, thetriboelectric material layer including a plurality of nanoscaleprotrusions extending outwardly therefrom, the triboelectric materiallayer including a first material that has a first position on atriboelectric series; (b) an elastic member having an undulated shapedisposed against the triboelectric material layer of the triboelectricmember, including a dielectric layer and a second conductive layerdisposed on the dielectric layer, the dielectric layer having anelasticity that results in the elastic member returning to the undulatedshape after being compressed, the second conductive layer including asecond material that has a second position, different from the firstposition, on the triboelectric series; (c) a first load that is inelectrical communication with the first conductive layer and with thesecond conductive layer, so that when a force drives the firsttriboelectric member against the elastic member, thereby compressing theelastic member, and after the force is released from the firsttriboelectric member charges will flow between the first conductivelayer and the second conductive layer through the load; (d) a secondtriboelectric member spaced apart from the first triboelectric member,including a fourth conductive layer and a triboelectric material layerdisposed on the third conductive layer, the triboelectric material layerincluding a plurality of nanoscale protrusions extending outwardlytherefrom, the triboelectric material layer including the firstmaterial, the second triboelectric member disposed so that the pluralityof nanoscale protrusions of the first triboelectric member face theplurality of nanoscale protrusions of the second triboelectric memberand so that the elastic member is disposed there-between; (e) a fourthconductive layer disposed on the dielectric layer opposite from thesecond conductive layer; and (f) a second load that is in electricalcommunication with the third conductive layer and with the fourthconductive layer.
 13. The electrical generator of claim 12, wherein thetriboelectric material layer comprises PTFE.
 14. The electricalgenerator of claim 12, wherein the first conductive layer comprisescopper.
 15. The electrical generator of claim 12, wherein the secondconductive layer comprises copper.
 16. The electrical generator of claim12, wherein the dielectric layer comprises a polyimide film.
 17. Amethod of making a triboelectric generator, comprising the steps of: (a)applying a first conductive layer on a selected surface of a firstsubstrate; (b) applying a triboelectric material on the conductivelayer, the triboelectric material layer including a first material thathas a first position on a triboelectric series, thereby generating afirst triboelectric member; (c) applying a second conductive layer to adielectric elastic material having a predefined shape, the secondconductive layer including a second material that has a second position,different from the first position, on the triboelectric series, thedielectric elastic material having an elasticity that results in theelastic member returning to the predefined shape after being compressed,thereby generating an elastic member; (d) placing the second conductivelayer of the elastic member against the triboelectric material of thefirst triboelectric member; and (e) electrically coupling a load betweenthe first conductive layer and the second conductive layer.
 18. Anmethod of claim 17, wherein the dielectric elastic material comprises apolyimide film and further comprising the step of making the predefinedshape of the dielectric elastic material into an undulated shape.
 19. Anmethod of claim 18, wherein the step of making the predefined shape ofthe dielectric elastic material into an undulated shape comprises thesteps of: (a) heating the polyimide film until the polyimide filmbecomes flexible (b) weaving the polyimide film between a plurality ofparallel metal rods; and (c) cooling the polyimide film.
 20. An methodof claim 17, further comprising the step of forming a nanoscale textureon the first triboelectric member.
 21. An method of claim 20, whereinthe step of forming a nanoscale texture comprises applying inductivelycoupled plasma etching to the first triboelectric member to produce aplurality of nanostructures outwardly therefrom.
 22. An method of claim17, wherein the elastic member is made by a process comprising the stepsof: (a) disposing a plurality of polystyrene spheres on a surface of asubstrate; (b) surrounding the polystyrene spheres with an uncured PDMSand curing the PDMS; (c) separating the PDMS from the polystyrenespheres, thereby generating a mold corresponding to portions of thepolystyrene spheres; (d) coating the mold with the second conductivelayer; (e) casting the mold with PDMS and curing the PDMS so as to formpartial PDMS spheres surrounded with the conductive film; and (f)removing the PDMS spheres surrounded with the conductive film from themold.
 23. An method of claim 22, wherein the second conductive layercomprises copper.